Government regulators in Canada are investigating a series of mysterious oil spills around tar sands operations in Alberta. Thick oil is gurgling up unexpectedly from the ground instead of flowing through the wells that were built to collect it.

The spills are raising questions about a technology that's rapidly expanding to extract fossil fuels that could ultimately end up in the controversial Keystone XL pipeline.

The extent of the spills is small, compared with the huge open pits and slag pools that dot the tar sands area. But they come from a type of operation that is usually less damaging to the landscape.

For the past 30 years, oil companies have been drilling wells to get at deeper tar sand deposits. Often they inject pressurized steam deep underground to loosen up the tar sands and extract thick oil called bitumen.

The bitumen is supposed to be pumped back up through the wells. But it doesn't always work that way.

"We've had incidents in the past where there's been an explosive blowout as a result of pressure building up and then moving up through the rock formations until it emerges at the surface," says Chris Severson-Baker, managing director of the Pembina Institute, an environmental think tank. The new situation "is a bit unusual in that when [the bitumen] reached the surface, it sort of oozed out as opposed to blowing out."

The first of these oozing incidents started in 2009. Government regulators spent several years trying to figure out what caused it. Cara Tobin, spokeswoman for the Alberta Energy Regulator, says they still don't know "whether it has to do with technology, operating practices, mechanical issues, geology — that sort of thing."

And as that investigation stretches on, the regulators have three more of these oozing incidents to deal with. They are all occurring inside the Cold Lake Air Weapons Range, an area that's off limits to casual visitors.

In total, these four seep sites have contaminated about 50 acres, Tobin says. The total volume of uncaptured bitumen is estimated at 950 cubic meters — which would be enough to fill a community swimming pool.

"It's all very slow-release, but they're all still ongoing," she says.

Tobin says the oil company has strung up absorbent boom and fences around the four spill areas in order to contain the damage.

"Unfortunately there have been some wildlife mortalities, including waterfowl, beavers, tadpoles, frogs, muskrats and shrews," Booth says. "But there are wildlife deterrents that are now in place and that should prevent any future wildlife mortalities from occurring."

Because the bitumen continues to ooze from the ground, there's no telling how long workers will have to manage the mess.

The company, Canadian Natural Resources Limited, didn't respond to an interview request, but it said in a statement that it has 120 people dedicated to the cleanup.

The sludge of oil on the surface is only part of the environmental impact. The thick oil could also create an environmental hazard as it passes up through more than a quarter of a mile of rock.

"Eventually it would come in contact with groundwater resources — the fresh groundwater resources that are close to the surface — which are the most valuable in the sense that they can be used for domestic drinking water and other purposes," says Severson-Baker from Pembina.

He's concerned about what will happen as this steam-pumping technology expands throughout the region to tap the vast tar sands resources there. If scientists don't understand why these four incidents occurred, he says, how can future problems be prevented?

These operations already have a big environmental impact because oil companies burn a lot of natural gas to generate the steam. So producing this kind of oil puts substantial amounts of carbon dioxide into the atmosphere before it's even burned.

These contamination issues add another wrinkle, "so it's really important to be able to understand under what circumstances those issues might occur in order to design projects that eliminate that risk," Severson-Baker says.

It's also a major test for Alberta's new oil-field regulators. The government there is pushing for the U.S. to approve the proposed Keystone XL pipeline, which would take diluted bitumen from this region to refineries in the United States. The environmental impact of tar sands operations have figured into the U.S. government's assessment of the pipeline.

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